Prolonged mental fatigue can impair self-control and increase aggression

Prolonged mental fatigue can exhaust brain regions essential to an individual's ability to self-control, leading people to behave more aggressively.

In a new interdisciplinary study published in PNASA group of researchers in neuroscience and economics at the IMT School of Advanced Studies Lucca has identified the controversial concept of “ego depletion”, i.e. the reduction in willpower caused by previous ego exploitation. It is associated with physical changes in the area it controls. Executive functions of the brain. In particular, in the awake brain, fatigue appears to correspond to an increase in EEG waves typical during sleep in the decision-making frontal cortical zone.

In the scientific literature, the so-called ego depletion theory emerged in the early 2000s. The underlying idea is that self-control is a limited cognitive resource for everyone, so the more you exercise it, the more you deplete it. The behavioral economics literature uses different types of cognitive operations typical of economic games to investigate the effects of ego depletion on behavior, such as reduced empathy for others and a reduced tendency to act altruistically. , or increased aggression.

However, in recent years this theory has been criticized. Subsequent studies have found that they have not always been able to replicate the effects of willpower “expenditure” on individuals engaged in intense cognitive tasks, or even if they have, the effects are much smaller. than the original estimate. Furthermore, the brain correlates of such effects remained unclear.

New research is tackling a classic problem by adding a neuroscience perspective. Sleep research has identified a phenomenon called “local sleep.” This occurs when some areas of a person's brain when they are awake begin to show typical neural activity seen during sleep on the EEG, namely delta waves. This has been shown to occur especially in cases of mental fatigue. “Our initial hypothesis was that localized sleep is a neuronal manifestation of the ego depletion phenomenon known in psychology,” said Erica Aldari, a researcher at the IMT School and first author of the paper. Observe.

To test this hypothesis, the researchers investigated how long the study would last for an hour, rather than the classic 15 minutes typically used in this type of research, to better clarify if any potential effects existed. A fatigue task was given to a group of individuals. Next, individuals played economic games that required varying degrees of aggression and cooperation, including the so-called hawk and dove game. The game involves sharing limited resources in a hostile environmental situation, forcing people to choose between cooperating or acting tyrannically, potentially resulting in resource loss for both parties. there is. Compared to a control group who did not undergo cognitive fatigue, those who underwent cognitive fatigue were found to be significantly more uncooperative and hostile. Specifically, the rate of peaceful cooperation decreased from 86 percent in the “no fatigue” group to 41 percent in the “fatigue” group (p>0.001, 447 total subjects).

All participants in the experiment (n=44) underwent an EEG test while playing an economic game. Consistent with the study's hypothesis, fatigued people showed the appearance of areas showing typical sleep waves in some areas of the frontal lobe, but not at all in other areas. did.

Our research shows that mental fatigue has a measurable impact on behavior, and once a certain degree of fatigue sets in, people are more likely to behave in a hostile manner. ”

Erica Ordali, IMT School Researcher, First Author

“These results show that metabolic fatigue within specific brain regions influences our decision-making processes, and provide a scientific basis for the conventional wisdom of 'trying to sleep' before making a decision.” ,” said study co-author and director Pietro Pietrini. A researcher at the Molecular Mind Lab at the IMT School, where this study was planned. “Overall, these findings show that when our brains are 'tired,' we may make choices that are even against our own interests, making us less likely to make economic transactions or legal agreements.” “In fact, this is what people do in most criminal acts as well,” Pietrini concludes.

The study was carried out by the IMT Lucca School of Advanced Studies in collaboration with researchers from the University of Florence.